The present invention relates to a turbocharger.
Some automobile engines employ turbochargers which compress air supplied to the engines using the pressure of exhaust gas to provide high power. Such turbochargers include turbochargers having a turbine shaft accompanied by a turbine wheel secured to one end thereof and a compressor impeller secured to another end thereof, a bearing device rotatably supporting the turbine shaft, and a bearing housing that houses the bearing device with the turbine wheel and the compressor impeller being exposed on both end surfaces in the axial direction thereof.
A turbocharger is configured to convert the pressure of exhaust gas into a rotational force using the turbine wheel and to compress air to be supplied to the engine using the compressor impeller which is rotated integrally with the turbine wheel by the turbine shaft. The turbine wheel is heated to a very high temperature because it is directly exposed to exhaust gas at a high temperature. The heat of the turbine wheel at the elevated temperature is transferred to the bearing device to increase the temperature of the same. The state of lubrication of the bearing device is consequently deteriorated, which can result in seizure of the device to reduce the durability of the same. For this reason, a turbocharger as described above normally has a configuration in which an engine oil or engine cooling water is circulated in the bearing housing containing the bearing device to cool the bearing device.
In addition to a cooling mechanism as described above, measures have been taken including the provision of a heat shield plate that is disposed between the turbine wheel and the bearing housing to prevent the heat of the turbine wheel from being transferred to the bearing device through the bearing housing (for example, see JP-A-2002-106569, JP-A-7-189724).
In the examples of the related art, although an extremely great temperature rise at the bearing device can be prevented by cooling the device with cooling water or using a heat shield plate, the suppression of a temperature rise is still insufficient in view of the durability of the bearing device to be maintained. Strong demands therefore remain for more effective measures to suppress a temperature rise at a bearing device for suppressing reduction in the durability of the bearing device.